1. Field of the Invention
The present invention relates to a technique for driving a hard disk, and more particularly to a technique for generating sector pulses.
2. Description of the Related Art
Hard disk drives have been widely used for an auxiliary memory which serves as a means for accessing a large quantity of data at a high rate in computer systems. For such hard disk drives, a "constant-density" recording method and a "zone-bit" recording method have been widely used. The constant-density recording method has been proposed by Mark S. Young, "Constant Density Recording Alive With New Chips", Electronic Design, page 141 to page 144. In accordance with the constant-density recording method, all tracks including radial inner tracks and radial outer tracks have substantially the same data density to improve the data capacity of compact disks. In accordance with the constant-density recording method, the data recording area on a magnetic disk is divided into a plurality of zones each having a constant recording density in a radial direction on the magnetic disk. Tracks of different zones are allocated different quantities of data sectors. In particular, tracks of radial outer zones have a larger number of data sectors than those of radial inner zones. On the other hand, the data sectors are substantially the same size irrespective of their positions on the magnetic disk. For this reason, servo sectors of different zones have different quantities of data sectors. The servo sectors are unit sectors each consisting of a servo domain, on which servo information is recorded, and a data sector, on which actual data is recorded. In this regard, the constant-density recording method has been widely used for hard disk drives because it can record a large quantity of information per track on a magnetic disk, as compared with other recording methods.
In a magnetic disk in accordance with the constant-density recording method, one data recording area of the magnetic disk corresponds to one frame. The data recording area is divided into three zones, namely, the first, second, and third zones, and a radial direction. That is, the first to third zones each have five data sectors, four data sectors, and three data sectors corresponding in number to the servo sectors. Here, "frames" means a plurality of areas divided from each track on a magnetic disk and a circumferential direction. Each frame has a certain number of servo sectors. The first frame of each track is called an index frame and the first servo sector of the index frame is called an index sector. The first servo sector of each frame following the index frame is called a servo index sector. Synchronous signals associated with the index sector and servo index sector are called index pulses. When a magnetic disk calls data sectors configured as noted above in the constant-density recording method, those data sectors have different positions and different areas of the magnetic disk. For this reason, it is necessary to provide the signal indicative of a reference position associate with the storing of data recording or readout when an access to the data on the magnetic disk is executed, namely, starting point of each data sector. Such a signal indicative of the starting point of a data sector is called a data sector pulse which hereinafter will be simply referred to as a sector pulse.
Generally, sector pulses are produced using software. A servo gate signal as a signal indicative of a servo zone. When a servo interrupt is generated during a high-level state of the servo gate signal, it is transmitted to an essential processing unit which in turn reads out a sector producing value from a random access memory. The central processing unit downloads the sector producing value in a register included in a sector pulse generating circuit. Under this condition, counting of input sector pulses is carried out from a negative edge of the servo gate signal. When the counter value is equal to the sector producing value, and desired output central pulse is generated.
In hard disk drives, CPU's control the hard disk drives and the production of sector pulses using software. However, CPU's may be overloaded due to the production of sector pulses using software in the case of higher-speed hard disk drive having a larger capacity.
The following patents each disclose features in common with the present invention but do not disclose the specific technique for generating sector pulses in accordance with the present invention as recited in the accompanying claims.
______________________________________ U.S. Pat. No. Inventor Date ______________________________________ 5,539,795 Takase July 23, 1996 5,517,371 Takei May 14, 1996 5,506,735 Okazaki April 9, 1996 5,479,301 Takeuchi December 26, 1995 5,442,499 Emori August 15, 1995 5,455,721 Nemazie et al. October 3, 1995 5,307,216 Cook et al. April 26, 1994 5,276,564 Hessing et al. January 4, 1994 4,797,757 Haitani January 10, 1989 4,757,406 Stewart et al. July 12, 1988 ______________________________________